1. Technical Field
A solution for platinum (abbreviated as “Pt”) chemical mechanical polishing (abbreviated as “CMP”) containing an alkali aqueous solution and an oxidizer is disclosed. More specifically, a method for forming Pt patterns including using the above Pt-CMP solution is disclosed which can improve a polishing rate and polishing characteristics of Pt used as a lower electrode of a metal capacitor.
2. Description of the Related Art
Platinum is a noble metal which is chemically and mechanically stable, and is an essential material used in fabricating high performance semiconductor devices. In addition, platinum (Pt) has been recently used as a lower electrode in DRAM devices. The lower electrode is created while forming metal layer/insulating film/metal layer-type capacitors through an electro-deposition process.
However, when the Pt layer is electro-deposited, the current is non-uniform due to the geometry and density of the oxide layer that is used for isolation. As a result, the Pt layer is non-uniformly formed and short-circuit is caused.
In order to solve the above-described problem, after the Pt layer is electro-deposited, a CMP process can be performed on the upper portion of the layer to planarize the Pt layer. However, because the Pt layer has relatively low chemical reactivity, appropriate CMP slurry cannot be provided to polish the Pt during CMP process. Thus, the common slurries intended for other metals such as tungsten or aluminum are employed when polishing platinum.
The slurries intended for other metals also include chemicals for planarizing of the various metal layers on a silicon substrate. In general, the slurry for a metal CMP process with a strong acidity of pH 2˜4 contains an abrasive such as alumina (Al2O3) or manganese oxide (MnO2) and an oxidizer such as hydrogen peroxide (H2O2) or ferric nitrate (Fe(NO3)2) as a first additive, using distilled water or ultra pure water. Further, a small amount of surfactant or dispersing agent may be added to improve CMP slurry properties.
Since the polishing speed of Pt layers is very slow, the CMP process is performed for a long period of time under high polishing pressure in order to adequately planarize the Pt.
As a result, the Pt layers may be separated from the interlayer insulating film because the Pt layer has poor adhesion to the interlayer insulating film. In addition, dishing and erosion effects are generated on the Pt layer adjacent to the interlayer insulating film.
Moreover, when the Pt layer is polished for a long time under high polishing pressure, the abrasive included in the slurry can severely scratch the interlayer insulating film, and impurities such as the slurry grounds can remain on the Pt layer. Therefore, the properties of the resultant device are compromised.